It is not recommended that you invade an enclosure (shimari) before you get strong on the outside. But with a strong position in the center and in the case when the influence Black gets is not going to help much, go for an invasion.
aLegendWai: Would anyone mind to tell me why an invasion is good if W's outside influence is strong (but far from the shimari)? You know, this invasion will never succeed. All invaded stones are going to be captured.
Is it used to create weakness (aji) for W to exploit?
If so, what if W tries approach shimari and threaten to invade inside (instead of invade directly)? In this case, W can expand and attack at the same time. What do you think?
I think the point is that the invasion can succeed
Here's something I remember from my first series of Go articles I read a quarter of a century ago.
But it is quite thin and if the surroundings are favourable, White has a possibility to cut and make a fight of it.
If is this atari, then White can make a ko-fight of it. Usually I consider this type of ko as an I-lose-nothing-ko, which is a very pleasant ko to fight. Any compensation for the group is good.
TDerz If White is considered very strong[1] at the outside, Black could also consider this move for defending (see sabaki for a continuation). I did a little bit of pattern searching on Jan's incredible database at
gobase.org because I was not so sure anymore whether Black should play like this, i.e. the 4-2 hane.
GoBase.org came up with several games, including one with the exact position:
These first three show the White kosumi-tesuji continuation on the 2-2 point: (1) Takagawa Kaku (B) vs. Kitani Minoru 1963-12; (2) Takagawa Kaku (B) vs. Kitani Minoru, 1964, 19th Honinbo League, Round 5; (3) Hotta Seiji vs. Hiroe Hiroyuki, 1990-02-22, 31st Okan,31, Japan, Round 2.
In the first two games Black is very, very strong on the outside - very different from the diagrams up here where White is strong - and White uses the 5-5 shimari reducing move first, i.e. before the displayed moves. Similar but a little bit less strong is the Black position in the third game.
(4) Ishida Atsushi (7p) vs. Kawamura Kazunori (8p), 22nd Tengen title, Prelim. rd. 1, game 11, 1996-03-07 is the only professional game which had a part of the upper position in actual play. This could mean that it is playable :-)
(5) Go Seigen, 3 dan vs. White Sekiyama Riichi, 4 dan, Oteai, 1930-04-02,03 in Round 5 (of 8) of spring session of the Nihon Ki-in Rating Tournament is one game with the position of the above ko diagram.
(6) 13th Japan-China Go Exchange, Round 1, Ma Xiaochun 9p vs. Ishida Akira 9p, 1985-05-28 shows one game where ko is avoided (Black was very strong in the shimari environment) and a different fight results.
[1] This way of playing seems more appropriate if Black, not White, is strong and has stones around the side-hoshis. See for example part 9 of Charles Matthews excellent 'Setpiece Kos' series. There, move 2 above leads to an interesting ko (colors reversed). In the next diagram you can see that the whole situation could also appear starting with at 3:
White will have played already a and b before starting to move into the corner.
All positions where White connects solidly are ones where White already has the circled or at least the squared peeping stone. White's options are thus cutting or living. White is strong in the surroundings and these moves therefore appear quite late in the games, much later than in the above examples. -- Tommie?
Dieter: I think this is not correct: Black will connect at a and White can only make an L+1-group with b. Next, Black kills playing c.
TDerz: Sloppy of me. Then I should better only state that the solid connection appears in professional games, e.g. no. (6) above and be silent about the reasons why they played it. If Black connects at a, then Black can be cut at d. If Black were connecting both at a and d, White could also play two moves b and e needed for living. As said above, the strong surroundings make the difference and this certainly cannot be generalized. It is fighting and can only be read out.
The this pattern appears often when black is strong. In fact, white will sometimes tenuki after this and come back to do something with it later. Calvin
This is a useful play to know about in the early endgame. It corrects the aji in the enclosure, when White is strong locally.
It's because protects the cut at a, right? - Fhayashi
I'd say it has more to do with playing safely at b, instead. -- Charles
TDerz The 2nd-line kosumi puzzled me. Would this one space extension, , do the same as above kosumi, S1?
I prefer over a.
The difference seems to be that in the case of and
, black seems to be obliged to play a, whereby White gets a forcing move at 4 (see next diagram below). If
here, then White can live with
and
because black's cut at b is not protected and he cannot play c.
The circled exchange could also happen without the stone present in first place! In this case I would prefer to play it further away from the shimari (x, y: later).
Bill: I confess to being flabbergasted by the discussion of the kosumi to the second line and the one space extension. Not by the plays, which may be best under certain circumstances, but by the diagrams showing them, in which they are almost certainly horrible plays.
Charles Bill, this would be another case, in which your implicit convention shows up. Sure, if there were no white stones at all in this quarter of the board, the diagonal to the second line is a sort of ridiculous, novice play. But obviously I didn't mean it that way. Do I really have to clip my diagrams down, to make them beyond criticism along these lines? I really don't believe that (as I wrote elsewhere) there is an SL convention that empty points are taken to be empty, rather than possible wild cards.
Bill: Even if the empty points are wild cards, the kosumi above doesn't make sense to me. If you are expecting the reader to fill in the appropriate surroundings, you are asking a lot, IMO. I see it as a question of clarity, not convention.
For instance, in this diagram White is strong locally, but
does not seem right. I know that is not what you meant, but that's my point. You and I and other dan players may be able to recognize situations where the kosumi is appropriate, but how about the average go player?
I do not think that clipping the diagrams would be much clearer, either. You are still relying upon the reader to fill in the blanks appropriately. Those who can do so probably do not need the advice.
Charles You know, I was shown this play by my national champion, a strong ama 6 dan. I assumed that passing it on might be of some help.
This is a common way of strengthening the corner. It is also questionable in this context <sigh>, but better.
TDerz Flabbergasted - me too! Such a nice, simple move. It has influence too. This is much more the move which will fit usually and cannot be bad.
This cap is also good for reducing black's expansion in a moyo game. Your opponent's good move is your good move.
Is there already a page for sequences starting from here= ?
Calvin This is covered under Probe.